1. Field of the Invention
The present invention relates to an improvement of a sheet distribution device which distributes and stores sheets discharged from an image forming device and performs a predetermined post-processing.
2. Description of the Related Art
As a sheet distribution device usually called "sorter", as disclosed, for example, in the Japanese Patent Application Laid-open No. Hei 4-43089, there is a known constitution in which a sheet with an image formed thereon (hereinafter, referred to as the printed sheet) discharged from a printer, a copying machine or another image forming device is successively distributed and accumulated by a sheet distribution means called "indexer" onto plural distribution bins (sorting trays). When the number of printed sheets accumulated on each distribution bin reaches a predetermined number, the bunch of sheets are bundled and stapled by using a stapler which can move vertically or horizontally (in a transverse direction of the sheet) along sheet receiving ends of plural distribution bins.
In the stapling process in which the stapler is used, the bunch of sheets on one of the distribution bins need to be selectively pushed out toward the stapler. For this purpose, in the conventional constitution, each distribution bin is constituted movable toward the stapler. Then, the distribution bin with the bunch of sheets to be stapled accumulated thereon are pushed out toward the stapler together with the bunch of sheets. Alternatively, each distribution bin is provided with a sheet bunch pushing member.
However, in the constitution in which the distribution bin can be moved toward the stapler, due consideration has to be given in order to avoid an interference of the distribution bin and the stapler. Not only in the constitution but also in the constitution in which each distribution bin is provided with the sheet bunch pushing member, a structure and drive system of the sheet distribution device are disadvantageously complicated.
To solve the problem, the applicant has proposed in the Japanese Patent Application Laid-open No. Hei 8-117514 a sheet bunch pushing device in which on a guide rail extended vertically through plural distribution bins provided is a sheet bunch pushing member for selectively pushing out toward a post-processing device a bunch of sheets on a predetermined distribution bin among the plural distribution bins. The sheet bunch pushing member is provided movable vertically along the guide rail.
In the proposed sheet bunch pushing device, the guide rail is provided in an opening which is formed in the distribution bin. The guide rail can be moved horizontally in the opening while keeping its perpendicularly raised condition. The sheet bunch pushing member is controlled to vertically move along the guide rail, while the guide rail itself is controlled to move horizontally together with the sheet bunch pushing member. Thereby, the bunch of sheets are selectively pushed out from one distribution bin to the post-processing device.
In the sheet bunch pushing device, when a movement locus of the sheet bunch pushing member is seen perpendicularly from the above, in a position in which the sheet bunch pushing member is farthest from the post-processing device (elevated or lowered vertically), the sheet bunch pushing member fails to overlap edges of the opening in the distribution bin. However, in a position (range) in which the sheet bunch pushing member pushes out the bunch of sheets, the sheet bunch pushing member overlaps one edge of the opening in the distribution bin. When the bunch of sheets on the distribution bin are pushed out by the sheet bunch pushing member, the distribution bin may be deflected or the sheets on the distribution bin may be deformed. Even in this case, by contacting all the sheets on the distribution bin in an engagement portion of the edge of the distribution bin and the sheet bunch pushing member (in the portion in which the edge and the sheet bunch pushing member slide against each other), the sheet bunch pushing member can securely push out all the sheets toward the post-processing device. In the portion where the edge of the distribution bin is engaged with the sheet bunch pushing member, at least a lower face (lower portion) of the sheet bunch pushing member is engaged with an upper face (upper portion) of the edge of the distribution bin. Alternatively, an upper face (upper portion) of the sheet bunch pushing member may abut on a lower face (lower portion) of the distribution bin just above the distribution bin from which the sheets are pushed out.
In the sheet bunch pushing device, when the sheet bunch pushing member is moved from one distribution bin to the next distribution bin, the sheet bunch pushing member is first retreated horizontally to a position where it is apart from the edge of the distribution bin. Subsequently, the sheet bunch pushing member is moved vertically along the guide rail. Further, the sheet bunch pushing member is moved horizontally to push out a bunch of sheets on the next distribution bin. Therefore, a horizontal movement distance of the sheet bunch pushing member is long. A period of time required for successively pushing out bunches of sheets accumulated on multiple distribution bins to the post-processing device is entirely prolonged. Consequently, there has been a demand for a reduction in time.